1. Field of the Invention
The present invention relates to an electrical connector that receives a printed circuit card and couples the printed circuit card electrically to a mother printed circuit board. More particularly, the present invention relates to an electrical connector having an alignment member for aligning the printed circuit card relative to the connector during insertion of the printed circuit card into the connector to align conductive pads on the printed circuit card with electrical contacts of the connector.
2. Background Information
It is well known to provide card-edge electrical connector sockets for electrically coupling a printed circuit card board to a main mother printed circuit board. As electrical components get smaller and smaller, spacing between contacts of the electrical connector and between the conductive pads on the printed circuit card is reduced. Tighter positional tolerances are required on the connector in order to ensure proper engagement between the contacts of the connector and the pads of the printed circuit card. It is known to replace some generally centralized pad positions in the printed circuit card with a slot or keyway that mates with an alignment post or key formed in the connector socket to provide polarization and alignment between the printed circuit card and the socket. The selected clearance gap between the keyway and the key, plus the manufacturing tolerances of both the keyway and the key, aligns the conductive pads of the printed circuit card with the contacts of the electrical connector closely enough to make a proper connection.
An exemplary add-in printed circuit card is the Accelerated Graphics Port (AGP) add-in card described in the Accelerated Graphics Port Interface Specification. Revision 2.0, Intel Corporation, May 4, 1998. (Available on the Worldwide Web at http://www.intel.com/pc-supp/platform/agfxport/index.htm) FIG. 1 is an exploded view showing a typical assembly of an AGP add-in card 20 to a mother board 10. The electrical connection between the printed circuit board and the mother board is provided by a connector 30. An AGP card has conductive pads along a portion of one edge for connection to the AGP bus through the connector. The connector has a pitch of 1.00 mm between centers of adjacent contacts allowing the overall length of the connector to be less than 75 mm. The fine pitch of the contacts requires that the use of a keyway to locate the pads relative to the connector contacts with great accuracy. The keyway 26 for the AGP add-in card is specified to have a width of 1.88+/xe2x88x920.05 mm. The key formed on the socket connector is specified to have a width of 1.78+/xe2x88x920.03 mm. Therefore, the clearance between the keyway formed in the add-in card and the key in the socket is 0.10 mm+/xe2x88x920.08 mm due to manufacturing tolerances. The keyway is the datum point for location of the pads when the printed circuit card in manufactured. The key is the datum point for the location of the contacts when the connector is manufactured. The mating of the keyway to the key aligns these two manufacturing datum points to within 0.18 mm.
Two types of AGP cards have been defined, a 3.3 volt card and a 1.5 volt card. The 3.3 volt card uses 3.3 volt signaling and operates at a bus speed of either 66 MHz or 133 MHz. The 1.5 volt card uses primarily 1.5 volt signaling, although clock and reset are 3.3 volts, and operates at a bus speed of 266 MHz. To prevent connection of a 3.3 volt AGP card to a 1.5 volt AGP bus or connection of a 1.5 volt AGP card to a 3.3 volt AGP bus, the alignment keys for the two cards are in different locations. FIG. 2 shows the connecting edge of a 3.3 volt card 20 and FIG. 4 shows the connecting edge of a 1.5 volt card 60. The specifications for both cards allow the same connector to be used for both cards by making the 1.5 volt card connector edge a 180xc2x0 rotation of the 3.3 volt card connector edge. In particular, the keyway 26 for the 3.3 volt card is located between pads 41 and 43 counting from the left of the component side; the 1.5 volt card keyway 66 is located between pads 41 and 43 counting from the right of the component side (pads 81 and 83 from the left).
The AGP architecture allows a motherboard to be constructed with a 3.3 volt AGP bus using a keyed connector so that only 3.3 volt AGP cards can be inserted into the connector. Likewise, a 1.5 volt AGP bus can be provided that accepts only 1.5 volt AGP cards using the same keyed connector installed with the opposite orientation. Thus, the keying provides polarization to prevent installation of printed circuit cards that are incompatible with the bus in addition to providing alignment of the manufacturing datum points. It is known to produce an AGP card that is compatible with both the 3.3 volt AGP bus and the 1.5 volt AGP bus where the card has two polarized keyways so that it may be inserted in either a 3.3 volt AGP connector or a 1.5 volt AGP connector.
An AGP bus can be designed that can electrically accommodate either a 3.3 volt only card or a 1.5 volt only card. However, the keying of the prior art prevents a single installed connector from accepting both types of cards. Accordingly, there is a need for a connector that can accept printed circuit cards with a variety of polarized keyings and still provide highly accurate positioning of the printed circuit card pads relative to the connector contacts.
A first aspect of the invention is an electrical connector that includes a housing formed to include first and second opposing ends and an elongated slot between the ends. The slot receives a connective edge of a printed circuit card. Closely spaced contacts located in the slot engage conductive pads on the printed circuit card. A first alignment member is formed integrally at the first end of the housing, to engage a non-polarized keyway during insertion of the printed circuit card into the elongated slot, aligning the printed circuit card relative to the contacts. A second aspect of the invention is the keying of the printed circuit card along a connective edge. The connective edge includes two connective regions which define a polarized keyway between the two connective regions. A third, non-connective, region located at one end of the connective regions defines a non-polarized keyway between the connective regions and the non-connective region. The polarized keyway is the dimensional datum point for fabrication of the printed circuit card and the non-polarized keyway is located precisely with reference to the polarized keyway. A third aspect of the invention is that different types of the printed circuit card, differentiated by the location of the polarized keyway, and the electrical connector form a system in which the connector may receive any of the types of the printed circuit card.